Currently there are several drugs in clinical use for the treatment of neurological and psychological disorders including schizophrenia, bipolor disorder, insomnia and anxiety disorders. Examples of these compounds include aripiprazole ziprasidone, and bifeprunox. The chemical structures of these compounds are given below.

Aripiprazole is an atypical antipsychotic used for the treatment of schizophrenia and schizoaffective disorder. Mace et al., CNS Drugs, 2009(23), 773-780. Other examples of heterocyclic derivatives that are useful for the treatment of schizophrenia are discussed in U.S. Pat. Nos. 5,350,747, 5,006,528, 7,160,888, and 6,127,357. PF-00217830 is another antipsychotic drug currently undergoing clinical studies for the treatment of schizophrenia. (NCT00580125) Other heterocyclic derivatives that have been stated to be useful as antipsychotic agents are those discussed in WO 93/04684, and European patent application EP 402644. However, many of the current antipsychotic drugs suffer from side effects and other undesirable drawbacks.
Aripiprazole is a dopamine partial agonist antipsychotic that is currently approved for clinical use in the United States and Europe. From the safety perspective it is remarkable that it is not highly sedative and does not impair the metabolic parameters. The advantages of a non-sedative and metabolically neutral antimanic drug are particularly relevant in the long-term, due to their impact on cognition and quality of life. (Vieta et al. Actas Esp Psiquiatr 2008:36(3):158-164). However, Aripiprazole is known to produce injection site reactions. (U.S. Pat. No. 7,115,587). Ziprasidone is an effective acute and long-term maintenance treatment option for patients with schizophrenia, schizoaffective disorder, and schizophric disorder. (Kutcher et al., Neuropsychiatr Dis Treat., 2005 1(2) 89-108). Ziprasidone users also suffer from multiple side effects including somnolence. Bifeprunox is known to improve symptoms in patients with schizophrenia. However, it also suffers from side effects such as weight gain an increase in cholesterol levels. (Barbato et al., WO 08/025781). Other antipsychotic agents also show substantial side effects. For example, paliperidone and riperidone are associated with weight gain in patients. (Nussbaum et al., Schizophrenia Bulletin 34(3) 419-422, 2008). Considering the range of side effects associated with current antipsychotic drugs, it is imperative to develop drugs with reduced side effects.
Optimization of a drug's bioavailability has many potential benefits. For patient convenience and enhanced compliance it is generally recognized that less frequent dosing is desirable. By extending the period through which the drug is released, a longer duration of action per dose is expected. This will then lead to an overall improvement of dosing parameters such as taking a drug once a day where it has previously required four times a day dosing or once a week or even less frequently when daily dosing was previously required. Many drugs are presently given at a once a day dosing frequency. Yet, not all of these drugs have pharmacokinetic properties that are suitable for dosing intervals of exactly twenty-four hours. Extending the period through which these drugs are released would also be beneficial.
One of the fundamental considerations in drug therapy involves the relationship between blood levels and therapeutic activity. For most drugs, it is of primary importance that serum levels remain between a minimally effective concentration and a potentially toxic level. In pharmacokinetic terms, the peaks and troughs of a drug's blood levels ideally fit well within the therapeutic window of serum concentrations. For certain therapeutic agents, this window is so narrow that dosage formulation becomes critical.
In an attempt to address the need for improved bioavailability, several drug release modulation technologies have been developed. Enteric coatings have been used as a protector of pharmaceuticals in the stomach and microencapsulating active agents using protenoid microspheres, liposomes or polysaccharides have been effective in abating enzyme degradation of the active agent. Enzyme inhibiting adjuvants have also been used to prevent enzyme degradation.
A wide range of pharmaceutical formulations provide sustained release through microencapsulation of the active agent in amides of dicarboxylic acids, modified amino acids or thermally condensed amino acids. Slow release rendering additives can also be intermixed with a large array of active agents in tablet formulations.
While microencapsulation and enteric coating technologies impart enhanced stability and time-release properties to active agent substances these technologies suffer from several shortcomings. Incorporation of the active agent is often dependent on diffusion into the microencapsulating matrix, which may not be quantitative and may complicate dosage reproducibility. In addition, encapsulated drugs rely on diffusion out of the matrix, degradation of the matrix, or both which is highly dependent the chemical properties and on the water solubility of the active agent. Conversely, water-soluble microspheres swell by an infinite degree and, unfortunately, may release the active agent in bursts with limited active agent available for sustained release. Furthermore, in some technologies, control of the degradation process required for active agent release is unreliable. Several implantable drug delivery systems have utilized polypeptide attachment to drugs. Additionally, other large polymeric carriers incorporating drugs into their matrices are used as implants for the gradual release of drug. Yet another technology combines the advantages of covalent drug attachment with liposome formation where the active ingredient is attached to highly ordered lipid films.
However, there is still a need for an active agent delivery system that is able to deliver certain active agents which have been heretofore not formulated or difficult to formulate in a sustained release formulation for release over a sustained period of time and which is convenient for patient dosing.
Self administered antipsychotic drugs often suffer from poor patient compliance in regular administration. Outpatients with schizophrenia often have problems complying with a regimen of oral antipsychotic medications. Bartko G et al., Psychiatry Research 1987 (22) 221-227. Thus, it is particularly useful to develop long acting antipsychotic drugs that can be administered less frequently.